The invention relates to a chuck for a winding apparatus for carrying and driving a core onto which a web is to be wound or rewound. The invention finds particular application in the rewinding industry, but is also applicable in other areas.
In the rewinding industry, differential winding is an industry wide term used for a system of rewinding flat sheet products (webs) onto tubes that support the finished product. The tubes are called cores and are usually made from cardboard or, more rarely, plastics, steel, aluminium, or composites. The flat sheet product, or web, can be anything supplied or used in reel, or roll, form. Paper, films, printed packaging and laminated products are most commonly processed. Usually the product is supplied for final rewinding onto cores from larger bulk reels or from a process machine.
The final rewinding process usually also involves another process called slitting, carried out using a combined slitter rewinder machine. This cuts the product formed in earlier processing into narrower widths. Typically, for example, a printing machine would produce printed packaging 1600 mm wide with a number of repeated patterns across its width. The slitting process cuts the full width into individual widths, typically for further use on subsequent machinery for packaging. Confectionery packaging for example uses this process.
After slitting, the individual widths are rewound either alternately onto two spaced, parallel rewinding shafts or side by side onto one shaft in known manner. A means of locating the cores into position and locking them onto the shaft or shafts is employed. The shaft or shafts is/are driven to provide tension, with the aim of enabling the product to be wound to with high quality and repeatability. The speed of processing is typically 7.5 m/s but in some machines is engineered to be 16.6 m/s. The main criterion for producing acceptable quality for the finished rolls is tension control.
Two systems exist for this. The first and generally the least sophisticated is termed as lock bar winding. This describes the cores being locked onto the rewind shaft and rotating in unison with it, the rewind shaft being driven by a drive motor. The sheet, or web, tension is thus distributed across the whole web width and is controlled by the drive motor torque. The torque is varied to give the desired winding tension and is usually varied to maintain a constant sheet tension throughout the reel as the diameter increases. Various means are available for establishing the roll diameter at any time during winding and this can be used to give increasing torque to the shaft to maintain a constant tension rewind as reel diameter increases during winding. Taper tension (decreasing web tension progressively) can also be used and gives reduced web tension proportionally as the reel diameter increases. Taken to the extreme this is sometimes termed constant torque winding.
The second means of rewinding is differential winding. This aims to compensate for variations in material parameters, such as thickness, across the web. Considering that several thousand layers of material can rewound onto a single reel, if there is a web thickness variation of just one micron, the resulting finished reel diameter can be significant. Lock bar winding has limitations due to this effect; when two or more reels are carried on one shaft, as the reel with the largest diameter due to thickness variation across the width of the supply web builds in diameter its web speed increases and this reel takes more tension, reducing the tension in the other reel on the same shaft. Differential winding allows each core to rotate at a different speed, however slight, and through the differential system aims to maintain a constant tension on each reel regardless of reel diameter.
There are many systems for differential winding available, but they all suffer in one or more areas with limitations as to their use. Typically a system consists of a driven shaft approximately 50 mm diameter (the most common core internal diameter=3xe2x80x3) with core holders positioned on the shaft line with the cores. Core position along the shaft is adjusted using plain spacers; either side of each core holder is a spacer.
The spacers are keyed to and driven by the shaft and the core holders are freely rotatable relative to the shaft, being supported on plain bearings, such as bronze, plastic or similar bushings. The core holders are separated from the spacers by friction elements and driven by torque transfer from the spacers via the friction elements.
The shaft is driven about 5% faster than the web speed. This is termed overspeed. It is advantageous to keep the overspeed as low as possible to reduce heating at the friction elements. In use, the shaft carries a stack of core holders and spacers along its length and a variable axial load can be applied to the stack. The driven spacers either side of each core holder are thus loaded axially on to the friction elements which in turn load the sides of the core holder to provide torque to the core. By varying the axial load the torque is varied to the core holders.
This conventional system has fundamental faults in trying to maintain a constant controllable rewind tension. One problem relates to the bushings within the core holders. Web tension is generated through friction from the bushings, which increases as the reel weight increases during winding and becomes an uncontrolled component of the tension.
Additionally, because the core holders are located axially, a tension gradient is produced along the shaft. The first core holder is loaded with all the axial force and when the tension required is very light the core holder at the other end of the shaft sees very little of the remaining force due to friction on the bushings and weight of the reels along the shaft. With more reels and weight the problem increases.
Other problems can be generated by the use of lay on rollers. These are used when high speed winding generates a layer of entrained air between layers of the reels. This layer of air acts as a lubricant affecting the stability of the reels, The lay on rollers are usually run on the upper surface of the reels under pressure to expel air, and this downward pressure also generates more unwanted tension in the rewind reels.
Set up time in adjusting the position of the core holders is also a restriction in the use of this conventional system. One known solution to this problem is to fill the shaft with core holders allowing the cores to be positioned anywhere along the shaft. The disadvantages of this arrangement include the across shaft tension difference, weight and cost.
Regarding the across shaft winding tension difference, this arises because of the larger number of core holders to be driven. If the core holders are driven as described above using a shaft end load to control drive torque, the core holders near to the shaft end where the end load is applied receive a larger end load and are therefore driven at higher torque than the core holders at the other end of the shaft.
Lubricants are sometimes employed to alleviate this effect but with detriment to hygiene. Problems can also arise as the (cardboard) cores commonly generate dust, which can contaminate any lubricant used.
A known design to overcome the problems of using shaft end load to control core torque is to use a separate form of core holder known as a differential chuck, and a corresponding shaft as described below. The driven shaft incorporates four air-inflatable flexible tubes along its length and corresponding friction segments which are pushed radially outwards by the tubes as they are inflated. Each differential chuck comprises a steel-lined inner surface on which the friction segments act to transfer torque from the shaft to the differential chuck. The force acting on the inner ring is proportional to the air pressure, which is controlled to control the torque transmitted evenly to all differential chucks on the shaft.
In such a design, each chuck is assembled on the shaft to form a complete unit and is fixed in position on the shaft to cooperate with a corresponding set of friction segments. In a rewinding machine a shaft may carry typically 80 chucks. This complete unit is termed a differential shaft. Two spaced, parallel differential shafts are typically fitted to a rewinder, conventionally termed a duplex rewinder.
A differential chuck must have an outside diameter smaller than the internal diameter of a core so that cores can be slid onto and off the differential shaft from its end, but must also grip the interior of the core during winding. To achieve this, each chuck is usually provided with a locking mechanism comprising cams which rise from the chuck outer surface to grip the surrounding core. The cams are driven by the shaft applying a torque to the chuck inner surface. A single direction locking mechanism is always used to ensure that when the cores are unlocked (by which time they may be carrying heavy reels of wound material) shaft or reel rotation in the opposite direction does not relock them. If a two-direction locking mechanism is used, a particular problem can arise because all of the chucks can only be driven either simultaneously or not at all. The problem arises when two cores are under the same reel and one unlocks while the other stays locked. Counter rotation will unlock the locked one but will inevitably lock the unlocked one, preventing reel removal.
The use of single direction locking chucks means that when it is necessary to reverse the winding direction of a differential shaft, it is necessary to dismantle the shaft and reverse the orientation of all of the chucks.
Other systems available can be called differential shafts. These have various designs but all rely on the shaft having built-in units providing radial force directly to the inside of the core with resultant core dust and friction problems with the cores running directly onto the shafts.
Low tension winding is often desirable for today""s materials but none of the conventional systems addresses this satisfactorily. For example, it is necessary to slit and rewind dye sheet for thermal colour printing before it can be used. Dye sheet may only be 3 micrometers thick and is slit into widths of only 15 to 30 cm. Very low winding tensions are required to handle narrow, delicate webs of this type, which are becoming more common as modern packaging and other industries develop, and existing winding shafts are unable to do this with sufficient consistency and accuracy. Also, all conventional systems suffer at least one of the problems of the need for clean, dust free operation, or the need to dismantle the winding shaft for reel width and direction changes.
The invention provides a chuck for a winding or rewinding apparatus and a method for mounting a core on a winding machine.
The invention may thus advantageously provide a chuck which can be switched between a first state, in which torque supplied by the drive shaft of a winding machine is transferred through the chuck to a core surrounding the chuck, and a second position in which the chuck does not engage the core and in which no torque can therefore be applied.
Further advantageously, the invention may provide a chuck in which this switching operation can be performed by an operator before cores are loaded onto a winding shaft (differential shaft) of a winding machine without any disassembly of the chucks or the shaft. In a preferred embodiment, the switching operation is achieved by locking an inner ring of each chuck by operating a torque-transfer element of the drive shaft, such as a friction segment, and rotating an outer casing of the chuck to a predetermined position or series of positions.
In a preferred embodiment, therefore, a row of chucks embodying the invention may be mounted on a differential shaft and a winding operation performed by pre-setting each chuck to an anticlockwise driving position, a clockwise driving position or an off position before cores are mounted on the shaft. The chucks can thus be switched so that a pre-selected number of the chucks within each core drives each core in order to enable a predetermined range of torque to be applied to each core during winding.
Further advantageously, the casing of the chuck embodying the invention may be mounted on the drive shaft by means of ball bearings, to reduce torque transfer due to friction.